1. Field of the Invention
The present invention relates generally to the field of fuel cells. More particularly, the present invention relates to a flat panel direct methanol fuel cell (DMFC) and method of making the same.
2. Description of the Prior Art
A fuel cell is an electrochemical cell in which a free energy change resulting from a fuel oxidation reaction is converted into electrical energy. Fuel cells utilizing methanol as fuel are typically called direct methanol fuel cells (DMFCs), which generate electricity by combining aqueous methanol with air. DMFC technology has become widely accepted as a viable fuel cell technology that offers itself to many application fields such as electronic apparatuses, vehicles, military equipment, the aerospace industry, and so on.
DMFCs, like ordinary batteries, provide DC electricity from two electrochemical reactions. These reactions occur at electrodes (or poles) to which reactants are continuously fed. The negative electrode (anode) is maintained by supplying methanol, whereas the positive electrode (cathode) is maintained by the supply of air. When providing current, methanol is electrochemically oxidized at the anode electrocatalyst to produce electrons, which travel through the external circuit to the cathode electrocatalyst where they are consumed together with oxygen in a reduction reaction. The circuit is maintained within the cell by the conduction of protons in the electrolyte. One molecule of methanol (CH3OH) and one molecule of water (H2O) together store six atoms of hydrogen. When fed as a mixture into a DMFC, they react to generate one molecule of CO2, 6 protons (H+), and 6 electrons to generate a flow of electric current. The protons and electrons generated by methanol and water react with oxygen to generate water. The methanol-water mixture provides an easy means of storing and transporting hydrogen, much better than storing liquid or gaseous hydrogen in storage tanks. Unlike hydrogen, methanol and water are liquids at room temperature and are easily stored in thin walled plastic containers. Therefore, DMFCs are lighter than their nearest rival hydrogen-air fuel cells.
In terms of the amount of electricity generated, a DMFC can currently generate 300-500 milliwatts per centimeter squared. The area of the cell size and the number of cells stacked together will provide the necessary power generation for whatever the watt and kilowatt needs are for vehicular and stationary applications.
FIG. 1 and FIG. 2 illustrates a conventional DMFC 10, wherein FIG. 1 is a plan view of the conventional DMFC 10 and FIG. 2 is a cross-sectional view of the conventional DMFC 10 along line I-I of FIG. 1. As shown in FIG. 1 and FIG. 2, the conventional DMFC 10 comprises a bipolar platelet assembly 12 and a fuel container 14. The bipolar platelet assembly 12 comprises an upper frame 51, lower frame 52, cathode wire lath 121, a plurality of bended bipolar wire laths 122, 123, 124, 125, an anode wire lath 126, and membrane electrode assemblies (MEAs) 131, 132, 133, 134, 135 interposed between corresponding wire laths.
The upper frame 51, the lower frame 52, the cathode wire lath 121, the plural bended bipolar wire laths 122, 123, 124, 125, the anode wire lath 126, and the MEAs 131, 132, 133, 134, 135 are adhesively stacked together to produce the stack structure as shown in FIG. 2. Typically, epoxy resin 53 or the like is used in between adjacent MEAs, thereby forming five basic cell units 21, 22, 23, 24 and 25. As known in the art, the cathode wire lath 121, bended bipolar wire laths 122, 123, 124, 125, and the anode wire lath 126 are titanium meshes treated by gold plating, and are therefore costly.
The basic cell unit 21 of the prior art DMFC 10 consists of the cathode wire lath 121, MEA 131, and the bended bipolar wire lath 122. The basic cell unit 22 consists of the bended bipolar wire lath 122, which functions as a cathode of the cell unit 22, MEA 132, and the bended bipolar wire lath 123, which functions as an anode of the cell unit 22. The basic cell unit 23 consists of the bended bipolar wire lath 123, which functions as a cathode of the cell unit 23, MEA 133, and the bended bipolar wire lath 124, which functions as an anode of the cell unit 23. The basic cell unit 24 consists of the bended bipolar wire lath 124, which functions as a cathode of the cell unit 24, MEA 134, and the bended bipolar wire lath 125, which functions as an anode of the cell unit 24. The basic cell unit 25 consists of the bended bipolar wire lath 125, which functions as a cathode of the cell unit 25, MEA 135, and the bended bipolar wire lath 126, which functions as an anode of the cell unit 25. Typically, each of the basic cell units 21, 22, 23, 24 and 25 provides a voltage of 0.6V, such that DMFC 10 comprising five serially connected basic cell units 21, 22, 23, 24 and 25 can provide a total voltage of 3.0V (0.6V×5=3.0V).
However, the above-described conventional DMFC 10 has several drawbacks. First, the bipolar platelet assembly 12 is too thick and thus unwieldy to carry. Furthermore, as mentioned, the cost of producing the conventional DMFC 10 is high since the cathode wire lath 121, bended bipolar wire laths 122, 123, 124, 125, and the anode wire lath 126 are titanium meshes treated by gold plating. Besides, the throughput of the conventional DMFC 10 is low because the bipolar wire laths 122, 123, 124, 125 are bended manually before mounting on the upper and lower frames. In light of the above, there is a need to provide a thin, inexpensive, and highly integrated DMFC that is conducive to mass production.